This invention relates to a projection optical system and a projection exposure apparatus using the same, and also to a device manufacturing method using such an apparatus. More particularly, the invention is suitably applicable to a projection exposure process for printing a reticle pattern on a photosensitive substrate in accordance with a step-and-repeat method or a step-and-scan method, for the manufacture of large-integration microdevices or semiconductor devices of a submicron or quarter-micron order, such as ICs, LSIs, CCDs, or liquid crystal panels, for example.
Generally, in a projection exposure apparatus, a reticle having an electronic circuit pattern formed thereon is illuminated with light (exposure light) from an illumination system (illumination optical system) and the pattern is projected onto a wafer through a projection optical system.
With increasing density of a semiconductor device, strict requirements have been applied to the performance or specification of a projection optical system. Generally, for a higher resolution, attempts have been made in relation to shortening the wavelength of exposure light, better correction of aberrations of a projection optical system, or enlargement of the numerical aperture (NA) of a projection optical system.
As regards the exposure light, light of an i-line lamp or laser light of an excimer laser such as KrF or ArF, or an F2 laser, for example, is used.
As regards enlargement of the numerical aperture (NA) of a projection optical system, the NA is being increased from 0.6 to 0.65, and then to 0.7.
As regards aberration correction, many attempts have been made so that a dual-telecentric system (being telecentric on object and image sides) is defined to reduce image distortion resulting from a warp of a reticle or a wafer and, on the other hand, distortion attributable to the projection optical system is reduced as much as possible. Also, that image plane width (field curvature amount) of best image points at each of the image heights is minimized, while the contrast gain at each of the image heights are made uniform as much as possible.
On the other hand, semiconductor device manufacturing processes use many reticle patterns or line widths and, in accordance with them, the illumination condition is changed variously to obtain a best pattern image. In order to minimize differences in distortion or image plane flatness, for example, under different illumination conditions, coma aberrations at each of the image heights are reduced to attain registration of the image plane.
Further, while the throughput of a projection exposure apparatus is an important factor, the chip size has been enlarged to increase the throughput. The exposure region of the projection optical system is enlarged to meet this.
As regards a projection optical system for use in a projection exposure apparatus, Japanese Laid-Open Patent Applications, Laid-Open No. 105861/1997, No. 48517/1998, and No. 79345/1998 have proposed a projection optical system wherein all lens systems are defined by spherical surfaces.
Japanese Published Patent Application, Publication No. 48089/1995 and Japanese Laid-Open Patent Applications, Laid-Open No. 128592/1995, No. 179204/1996, No. 34593/1993, No. 197791/1998, No. 154657/1998, No. 325922/1998, No. 333030/1998, and No. 6957/1999, have proposed a projection optical system wherein an aspherical surface is used for aberration correction.
It is an object of the present invention to provide a projection optical system by which aberrations such as distortion, curvature of field, astigmatism, coma and spherical aberration can be corrected satisfactorily such that a high optical performance is assured through an exposure region, and by which enlargement of numerical aperture (NA) and enlargement of exposure area can be attained.
It is another object of the present invention to provide a projection exposure apparatus having such a projection optical system.
It is a further object of the present invention to provide a device manufacturing method using such a projection exposure apparatus.
In accordance with an aspect of the present invention, there is provided a projection optical system for projecting an image of an object onto a photosensitive substrate, wherein said projection optical system includes at least one aspherical surface lens having aspherical surfaces formed on both sides thereof.
In one preferred form of this aspect of the present invention, each aspherical surface of said projection optical system satisfies a relation |xcex94ASPH/L| greater than 1xc3x9710xe2x88x926 where xcex94ASPH is the aspherical amount of the aspherical surface and L is an object-to-image distance of said projection optical system.
Here, the aspherical amount refers to a deviation between a spherical surface, following a design curvature radius, and an aspherical surface with respect to an optical axis direction.
The projection optical system may comprise a plurality of lens groups including a positive refractive power lens group and a negative refractive power lens group, and a relation |Lxxc3x80| greater than 17 may be satisfied where L is a conjugate distance of said projection optical system and xc3x80 is the sum of powers of the negative lens group or groups.
The aspherical surface may be formed on a surface satisfying a relation |hb/h| greater than 0.35 where h is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
The projection optical system may include two aspherical surfaces having regions in which their local curvature powers change with mutually opposite signs, from a surface center to a surface peripheral portion.
The two aspherical surfaces may be the surfaces on both sides of said aspherical surface lens.
Each aspherical surface of said projection optical system may satisfy a relation |xcex94ASPH/L| less than 0.02 where xcex94ASPH is the aspherical amount of the aspherical surface and L is an object-to-image distance of said projection optical system.
The projection optical system may comprise a plurality of lens groups including a positive refractive power lens group and a negative refractive power lens group, wherein a relation |Lxxc3x80| less than 70 is satisfied where L is a conjugate distance of said projection optical system and xc3x80 is the sum of powers of the negative lens group.
The aspherical surface may be formed on a surface satisfying a relation |hb/h| less than 15 where h is a height of an axial marginal light ray, and hb is a height of a most abaxial chief ray.
The projection optical system may be made a telecentric system both on the object side and on the image side.
Each aspherical surface lens of said projection optical system may have aspherical surfaces formed on both sides thereof.
In accordance with another aspect of the present invention, there is provided a projection exposure apparatus including a projection optical system as recited above.
In accordance with a further aspect of the present invention, there is provided a device manufacturing method for projecting a pattern of a reticle onto a wafer by use of a projection optical exposure apparatus as recited above, and for producing a device through a development process to the wafer.